The present invention relates to a heat exchanger preferably used as, for example, a heater core to be incorporated into a car air conditioner for a vehicle, and to a method of manufacturing the same.
A heat exchanger is widely used as a heater core for a car air conditioner for heating the interior of a vehicle compartment by making use of warm cooling water for cooling an engine. Such a heat exchanger includes a pair of header tanks spaced apart from each other; a plurality of flat heat exchange tubes which are disposed between the two header tanks at predetermined intervals along a longitudinal direction of the header tanks with their width direction coinciding with an air flow direction and whose opposite end portions are connected to the corresponding header tanks; and a plurality of corrugate fins each disposed between the adjacent heat exchange tubes.
Each header tank of a heat exchanger of such a type includes a box-shaped, rectangular parallelepiped tank body which opens toward the other header tank, and a header plate brazed to an open end portion of the tank body and closing the opening of the tank body. The tank body and the header plate are each formed by means of bending a metal blank. The tank body includes a rectangular top wall; a pair of first side walls extending from one pair of parallel sides of the top wall; and a pair of second side walls extending from the other pair of parallel sides of the top wall. Of the adjacent first and second side walls of the tank body, the first side wall has a joining portion which is formed integrally with the first side wall via a rounded connection portion and which extends along the inner surface of the second side wall. The header plate includes a rectangular closure wall having a plurality of tube insertion holes; a pair of first side walls extending from one pair of parallel sides of the closure wall and extending along the outer surfaces of opening-side end portions of the first side walls of the tank body; and a pair of second side walls extending from the other pair of parallel sides of the closure wall and extending along the outer surfaces of opening-side end portions of the second side walls of the tank body (see Japanese Patent Application Laid-Open (kokai) No. H8-226786).
However, since the header tanks described in the publication are formed by means of bending metal plates, relatively large recesses are unavoidably formed between the outer surfaces of the rounded connection portions of the tank body and tip end surfaces of the bent portions. As a result, at portions where the above-mentioned recesses are present, relatively large clearances are present between the first and second side walls of the tank body and the first and second side walls of the header plate, and brazing failure may occur between the tank body and the header plate. Such brazing failure must be repaired at a later time, and the repair work is troublesome.